Conventional Thin Film Transistors (TFTs) predominantly use, in the semiconductor layer, silicon such as an amorphous silicon thin film and a polycrystalline silicon thin film which is formed through polycrystallization of an amorphous silicon thin film using an excimer laser and so on.
In recent years, much focus has been placed on amorphous metal oxide semiconductors as a semiconductor layer for next-generation TFTs. In terms of transparency, such semiconductors show promise for application to displays, electronic paper, and so on. Even in terms of mobility, such semiconductors are also materials which can realize the 3 to 20 cm2/Vs required by high-performance liquid crystal and organic Electro-Luminescence (EL).
An amorphous indium zinc oxide semiconductor (a-InZnO) including indium (In) and zinc (Zn), an amorphous indium Gallium zinc oxide semiconductor (a-InGaZnO) which further includes gallium (Ga) as one more type of metal component, and so on, are known as representatives of amorphous metal oxide semiconductors.
Meanwhile, the sputtering method, which forms a film from vapor, and the sol-gel method, which forms a film from a solution, are representative methods for manufacturing a semiconductor layer (See PTL 1, PTL 2, and PTL 3, for example). The latter is characterized in being applicable to substrates with large surface areas and substrates with complex shapes.
The sol-gel method is a method in which a solution is prepared that includes, for each component metal of a metal oxide, a precursor which is a hydrolyzable organic compound, the solution undergoes hydrolysis reaction and polycondensation reaction to form a gel that has lost fluidity, and the gel is thermal-annealed to obtain a solid metal oxide. Metal alkoxides, and the like, are given as precursors. Water for the hydrolysis reaction and catalysts such as an acid, base, and so on, for controlling the hydrolysis reaction and the polycondensation reaction are further added to the precursor solution.